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Published October 21, 2009 | Supplemental Material
Journal Article Open

Electron-transfer processes in metal-free tetraferrocenylporphyrin. Understanding internal interactions to access mixed-valence States potentially useful for quantum cellular automata

Abstract

Redox properties of H_2TFcP [TFcP^(2-) = 5,10,15,20-tetraferrocenylporphyrin^(2-)] were investigated using cyclic voltammetry, differential pulse voltammetry, and square-wave voltammetry methods in a large variety of solvents and electrolytes. When DMF, THF, and MeCN were used with TBAP as the supporting electrolyte, the first oxidation wave was assigned to a single four-electron oxidation process reflecting simultaneous oxidation of all iron(II) centers into iron(III) centers in H_2TFcP. When an o-DCB (1,2-dichlorobenzene)/TBAP combination was used in electrochemical experiments, four ferrocene substituents underwent two very diffuse, "two-electron" stepwise oxidations. The use of a weakly coordinating TFAB ([NBu_4][B(C_6F_5)_4]) electrolyte in o-DCB or DCM results in four single-electron oxidation processes for ferrocene substituents in which the first and second single-electron waves have a relatively large separation, while the second, third, and fourth oxidation processes are more closely spaced; similar results were observed when a DCM/TBAP system and an imidazolium cation-based ionic liquid ((bmim)Tf_2N = N-butyl-N'-methylimidazolium bis(trifluoromethanesulfonyl)imide) were used. Spectroelectrochemical oxidation of H_2TFcP in o-DCB or DCM with TFAB as the supporting electrolyte allowed for characterization of the mixed-valence [H_2TFcP]^+, [H_2TFcP]^(2+), and [H_2TFcP]^(3+) compounds by UV-vis spectroscopy in addition to the "all-Fe(III)" [H_2TFcP]^(4+). The chemical oxidation of H_2TFcP was tested using a variety of oxidants which resulted in formation of mixed-valence [H_2TFcP]^+ and [H_2TFcP]^(2+) as well as [H_2TFcP]^(4+), which were characterized by UV-vis-NIR, MCD, IR, Mossbauer, and XPS spectroscopy. The intervalence-charge-transfer bands observed in the near-IR region in [H_2TFcP]^+ and [H_2TFcP]^(2+) complexes were analyzed using Hush formalism and found to be of class II (in Robin-Day classification) character with localized ferrous and ferric centers. Class II behavior of [H_2TFcP]^+ and [H_2TFcP]^(2+) complexes was further confirmed by Mossbauer, IR, and XPS data.

Additional Information

© 2009 American Chemical Society. Received July 1, 2009. Generous support from the NSF (Grant CHE-0809203) and Minnesota Supercomputing Institute to V.N.N. as well as University of Minnesota—Duluth Undergraduate Research Opportunity Grants to R.G.H. and C.B. is greatly appreciated. We also thank Dr. N. Kobayashi for the possibility to collect preliminary MCD data on H_2TFcP and Dr. R. Belosludov for help with the DFT calculations.

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